This invention relates to material examination techniques and, more particularly, to an inspection process indicating the existence of cracks, fissures and other such faults on solid surfaces.
Integrated circuit semiconductor electronic components are normally encapsulated in a ceramic or other suitable material for preventing electronic component deterioration resulting from, among other factors, dirt, dust, humidity and/or temperature fluctuations. To insure the physical integrity of the encapsulation, it is customary to inspect the components for the purpose of detecting cracks, fissures and other such faults with a view toward separating the defective from the physically sound products.
Various techniques of crack detection are known by those skilled in the art. U.S. Pat. No. 3,904,545 to Molina is exemplary of the class of penetrant-inspection methods which rely on the visibility of a liquid dye that penetrates into the cracks, fissures and other such faults.
U.S. Pat. No. 2,765,652 to Levengood teaches a crack detection method where the test surface is coated with a liquid silvering solution. Here the cracks, fissures and other such faults are indicated because they remain free from any overlaying by the silvering solution.
U.S. Pat. No. 1,640,567 to Firestone is representative of the photoelectric class of fault indicating techniques. Firestone teaches the use of a microscope, a photocell and associated circuitry responsive to the differential reflectivity of the test surface being examined; a fault condition being indicated by the unequal reflection of incident light.
The prior art techniques tend to be slow, invasive, costly and somewhat ineffective. For example, with the use of dye penetrant indicating techniques, difficulties arise in removing the dye penetrants often requiring extensive cleaning procedures. The photoelectric techniques are undesirable, inter alia, since they require the use of relatively elaborate apparatus which is unsuitable for on-the-spot field use.